Preparation of pigments



' Nov. 9, 1943. l. E. MUSKAT PREPARATION OF PIGMENTS Filed April 25, 1941 INVENTOR. \RVING E. MUSKAT Z MJM ATTORNEY.

ast rs. 9,194;

2,333,948 PREPARATION or lPIGMENT s v Irving E. Muslrat, Akron,

Plate Glass Companyiburgh Ohio, assignor to Pitts- Allegheny County,

This invention relates to the production of finely divided metallic oxides fromv the 'corresponding halides mally decomposed and is particularly'related to theproduction'of titanium dioxide pigments containing other metallic oxides. v

In my prior application for 'United States Let- .ters Patent, Serial No. 176,66, filed November 26, 1937, issued April 29, 1941, as U. S. Patent No. 2,240,343, or: tinuation-in-part, methods have been described and claimed wherein titanium halides are therunder conditions such that crystal formation is substantially minimized. In such application action of titanium tetrachloride with oxygen a crystalline form of titanium dioxide which is not useful" as a pigment isgenerally obtained and that this formation of crystalline titanium dioxide'may be prevented or substantially minimized by conducting the reaction out of contact with hot surfaces.

. bismuth, or antimony hich thisapplication is a conchlorides maybe decom-l 1 posed by this means. The incorporation of these agents serves .not only to improve. or change the color of the titanium dioxide but also acts to produce. products of more uniform, chalking characteristics, oil absorption, 1 to improve various other characteristics of the pigment." In any event, the process should be conducted in a mannersuch that the thermal decomposition occurs in vapor phase out of contact with hot surfaces within the reaction chamber in order to minimize the formation of seed crystals which' promote it was pointed out that upon reinto the reaction chamber through this gaseous 20- Accordingly, methods were described whereby the reaction might be conducted in vapor phase and the reaction adjacent hot walls or other hot surfaces within the reaction chamber substantially-minimized.

In accordance with the present invention, it has been noted that'similar difllculties are encountered in the treatment of other metal halides whichare capable of reacting with 'o'xygen or oxygen containinggases to form the correspond-' ing metallic oxides. Thus, when the halides of. aluminum, zinc, antimony, zirconium, chromium (including chromic, chromous and'chromyl chlo rides), cobalt, silicon, beryllium; boron,.cadmium, enum, nickel, vanadium, etc., aswell as titanium, are converted to the oxides, coarse crystalline materials are frequently. produced.

By conducting the reactionin vapor phase out of the formation of the crystalline form of oxide.

tallic halide it is usually'deslred to maintain a body of inert or non-oxidizing gas,ad 1acent the inlet whereby the incoming halide is introduced medium and the inlet itself is maintained out of substantial contact with the. oxidizing atmos'- phere. Y

s may be done, for examplaby introducing vaporized halide through a nozzle, establishing an atmosphere of inertgastherearound and con- .tinuously introducing enough inert gas to move a stream of the gas and the vapor from the nozzle into the oxidizing atmosphere. In accordance with'another method, the metallic halide in liquid contact with the hot furnace walls or other hot surfaces, a uniform,

obtained. L The invention is particularly applicable to the production of mixtures of halides to form blended finely divided oxide may be pigments, preferably titanium dioxide pigments.

For example, white pigments may be prepared by thermally decomposing a mixture of titanium tetrachloride and a; metallic halide such as zinc chloride, aluminum chlorid, or silicon .tetrachloride with oxygen containing gases./Simi-- .larly, a tinted pigment maybe secured by decomposition of a titanium halide in thepresence of a. chloride of amet al capable of forming a color oxide such as c romicchloride, chromylchloride, cobalt chloride vanadium chloride, etc. Likewise, the chlorides of other metals suchaslead, 55"

or solid state may be showered through an inert atmosphere and thence into an oxidizing zone. Nitrogen, carbon dioxide, helium or chlorine may be used as an inert gas for thisjprocess;

The temperature at which the decomposition is conducted is preferably maintained at about 1400 to 2200 F. While, higher temperatures may be used, coarsening of the product generally ocours to an undesirable degree. I

, -'The'accompa'nying drawing is a diagrammatic sectional vie'w'of an illustrative form o'fapparatus which is suitable for use in accordance with the present invention. In this' embodiment, I

providea verticallyarranged fuma'ce I, which I is equipped with a reaction chamber l 2, and pre-' heating zone 8. Suitableheating elements (not shown) are provided adjacent the preheating chamber 8, and the furnace may be covered par 'tiallyor completely with insulation. Ve rti cally disposed, concentrically arranged tubes 5 and ii' extend through the preheating zone andinto reaction space. h

In the operation of this device a stream of pre heat'ed metallic halide vapor such as a-mixture of'vaporizedtitanimn tetrachloride and silicon,

the

cobalt, orzmc chlorides, is introduced into tube.

particle size, and

v "In order to inhibit formation of crystals at the point of introduction of the me- I oxygen is admitted at" inlet 9.

a and nitrogen or other inert gas, introduced into tube 8 through inlettube l, ,while a stream of I The gases passing through the preheating zone are heated to reaction temperature. Thermal. decomposition of'the chlorides at the terminal portion. of tube is ofthe oxide. Heat may be applied to the filtration chamber, if necessary, in order tomaintain the temperature at the required value. In order to maintain the process in substantially .con-

prevented by the fiuid envelope'of inert gas which is discharged from tube 6, about the end qftube 5, thus preventing an accumulation of oxygen adjacent the metallic chloride iet. The'chloride vapor is thus swept into reaction zone 12, of

suitable size sucl'f that the chloride isdecomposed before substantial contact with the hot walls of the chamber can occur. It-will thus be apparentthat the-reaction of chloride and the oxygen is efiected in the vapor phase .and that the reaction is conducted in a manner such' that contact of the chloride adjacent .the hot surfaces withinthe chamber is substantially minimized in order to prevent or minimize formation of crystalline metallic oxides.

It should .be understood that the method of preparing metallic oxides. as describedherein is merely illustrative and that various other methods of decomposing the chloride herein mentionedmay be used. For example, the process may be conducted by introducing streams of vaporized titanium 'tetrahalide or other halide and oxygen or air in opposite directions into areaction chamber and withdrawing the productssof reaction along the halide inletwhereby an envelope. of

the evolved halogen such as chlorine is formed. about'the inlet. This process is described in copending application,- Serial No. 271,694, filed May 4, 1 939, by myself and Alphonse Pechukas.

As a further meansof insu'ringthe production of a finely divided product and minimizing formation of. crytals;.it is generally desirable to main-- tain the temperature of the'walls. of the reaction chamber substantially below the temperature of the main reaction zone, Thus, while the tem-. perature in the centralportion of the chamber where the major portion of the reaction occurs may be 900 to 1-200 C'., the temperature '(01' the walls is generally maintained below 850 C; and

,tinuous operation, a plurality of chambers I5, may be provided together with means for changing the fiow of the gases containing the oxides from one chamber toanother when one chamber has become filled.

When the-chamber is so filled or the filter becomes clogged, fiow of the suspensionto the chamber is discontinued and air, oxygen, or inert gas is introduced in order to remove adsorbed chlorine face thereof and the filter is thereby cleaned for further 'use. Thereafter, the oxides may be removed through a suitable outlet, such as outlet l'l.

provided at the top of the chamber, or, if desired, through a discharge chute provided at the bottom of the chamber. If desired, the calcination may be efiected by heating the air or inert'gas which is passed through the chamber to a'suitable temperature, for example, 750 C. This caicinationmay be continued until the chlorineand other impurities are driven ofl. Two hours at 600 C. is found to be suitable for most puroften 750 C. or below. The reaction zonemay be of any convenient size suflicient to prevent de; composition of the halide adjacent the surface thereof. The actual size required varies with the size of the oxygen and metal halide inlets and with the rate. of introduction of the reactants,

and accordingly, nospecific figures may beset forth. Generally speaking, 'however, if crystals are formed to any substantial degree, the reaction zone should be enlarged.

poses.

In accordance with .a further modification, method'sother than filtration may be utilized to remove suspended oxides. For example, they may be precipitated by subjection of the gases to supersonic vibrations such, as: are obtained from a quartz crystal, or to electrostatic or electromagnetic precipitation.

Th amount of other metallic halide used in conjunction with titanium tetrachloride may be varied in accordance with the results desired. In

many cases only small quantities, for example, 0.001 to one percent by weight based upon the weight of titanium halide is found necessary.

Thus, it is found that such small amounts of compounds such as cobalt chloride, molybdenum The exhaust gases containing chlorine and suspended metallic oxides are conveyed to a filter.

chamber l5, whichis provided with a suitable filter M. This filter may be of"any convenien't structure such as a plate or tube filter. 'I'hisfilter the production of colored pigments are desirable and accordingly, the amount of other metal oxide may comprise porousalundum, porous carborunl dum, or other resistant porous filter medium. In

accordance with a convenient modification, the filter may comprise a plurality of porous aluminum oxide'filter candles whereby the gases may be withdrawn through the walls thereof into the interior of the candle and may be subsequently discharged; In such'a case the oxides may be collected on the exterior side of the candle. As described ina copending application of Alphonse Pechukas and George Atkinson, Serial No. 386,863, filed April -i, 1941, care should be taken to insure the removal of the oxides from the gases while the temperature of the gases remains above about 250 C. in order to improve thequality and color chloride, silicontetrachloride, etc., may materially improve the characteristics (whiteness, particle size, etc.) of titanium dioxide. In ot'her cases,

incorporated will depend upon the color desired. Thus, increased quantities of pigmentaryproducts or halides capable of forming oxides such as chromium, nickel, copper, silicon, zinc, zirconium,

aluminum chloride, or other chloride, may be added .in somewhat larger quantities to produce a tinted or an extended. pigment. In such a case 'it is desirable to use sufilcient titanium tetrachloride to insure the presence of at least 30 percent titanium dioxide in the final pigment. Mixtures of titanium chloride with titanium bromides, fluorides, and iodides may be used as well as halides of other metals. The mixtures of halides may be formed by passing heated vaporized titanium tetrachloride over the other halide at a temperatur sufiiciently high to vaporiz said other 'chromium nickehcopper. alumiiiumetci, maybe addedas sulphides, sulphates orother salts; Simthe added agent may be introduced as an theadded agent is 2',s's otherfhalide or the halides ma waporizedandmixeda The decomposition of the halides'niay be 001? llic salts ducted in the presence of added meta than halides. ;T lius,'- cobalt, antimony.

ilariy,

oxide or in ,the free metallic state. The'decomposition is conduc or a metallic oxide,- sulphide or other non-halide;

agent is introduced into contacts the oxygen. In this case-it win 5 verted to the oxide subsequently.

\ While the to the production or a blended titanium pigment, titanium-free, finely divided metal oxides maybe prepared in accordance with the present invention. For example,-'theindividual above-mew tionedihalides 'may be decomposed alone or as r e .con-

- mixtures to producevarious desirable products.

In" such a case, the reaction-temperature may;

vary considerablywith the nature of the halide.

*Some halides willreact-with oxygen. readily at 100 F. while others may require temperatures ,in excess o! 2500 FI As will be understood by one skilled in the art,-the process is especially suitable for the halides. or the a'mphoteric, metals,

the halides o to oxides.

The following examples are illustrative:

- Example I Ana-pp wherein the diameter of the TiCli inlet was $4:

inch, the diameter of the inert gas inlet inch and the reaction zone, 4 inch es in diameter washeated toa temperature or 1000 C. A vaporized mixture comprising and 2 percent by vv0 was introduced intother 'oi ,10 liters 'per minute while oxygen was intro-f duced at a rate of 1-2 liters per minute and nitrogen at a rate of 4 liters per minute. The pigment suspension waswithdrawn and filtered at a temperature oi 450-C. Upon calcination oi the resultin'g'plgment, a white product of fine particle size was secured.

" --Ezample II An apparatus similar to that, shown in the drawingwas used .in which the'TiCh inlet was in diameter, the inert gas inlet was V2" and thereaction zone was 16" in diameter. This apparatus was heated' to 1000 C. and vaporized .TiCh containing 0.001 percent cobalt chloride was passed in at the rate of 10 litersper minute, nitrogen at the rate of 4 liters per minute and air at the rate of 60 liters per minute. The TiOz pig ment produced was withdrawn and filtered while hot. Upon calcination at 600 C., a white product having a blue undertone and having excellent pigmentary properties was obtained.

Example III An apparatus as described in application Serial No.--271,694, filed May 4, 1939, wasused having a reaction zone 14 inches in diameter. Air was passed to the reaction zone at a rate 01170 liters per minute A counter-current direction with respectto the air through a tube inch in internal diameter at arate of 12 liters per minute. The temperature was maintained at 1800 F. The titanium dioxide,

ted at temperatures at which in vapor state. When a metal J y the reaction zone it may be first-halogenated by the-free. halogenbeiore itinvention is particularlyapplicable i which are morereadily converted aratus such a illustrated in-the' drawing a 98 percent by volume'of TiClr lume of silicon tetrachloride eaction zone at 'asrat'e TiCh vapor was introduced in 1 chlorine', and residual components of theair were withdrawn to a settling'chamber where the T: ---was recovered. Aiter continuous operation ior 5% hours, a yield of 96 percent was'obtained, if The pigment was uniformly fine in texture.

Ekcample IV ess describedin Example III 'p'eated using a reaction zone having an internal 10 diameter of 4 inches through which air was in-' ,tIOdllCd at a rate of 28 liters per. minute. The titanium tetrachloride was introduced through a tube having a diameter of 0.5 inch at a rate of 30 .grams per minute. .The temperature was maintained at 1800 F. through the duration of the reaction. The product was veryflne and possessed a good color. The amount-of coarse crystals iormedwas below 0.5 percent of the total {T102 iormed. 2

Example V The apparatus describe used to decompose aluminum hloride. Aluminum chloride vapor at a temperature or 300C; was passedinto the reaction chamber at a rateof 8- -9liters per minute. Oxygen was passed in at the rate of 10 liters per minute, and nitrogen was added through the inert gas jet at the rate of '3 liters per minute, and the temperature within; the reaction zone was maintained at 900 to' 95080. The aluminumoxide was-co ected in thesettling chamber and was calcined for one hour-at 500 C. i i-the, presence of oxygen to remove traces oii-chlorine.

\ i 7 Example v1 i 'The apparatus described in Example 11 was used to prepare apigmentary zinc oxide 'coritaining substantial quahtities of silicon dioxide. A vaporized stream of' zin'c chloride which con- 40 tained'ab'out lB-percent silicon tetrachloride ,was'

passed into the reaction chamber at the rate .of 8 liters per minute. The reaction vessel was'maintained at 900 F. Air was' introduced at the rate 1 of 5liters perminute and chlorine was passed in through the inert .gas jet atythe rate of 2 .liters per minute. Afinely divided oxide'compositionwas collected in the settlingchamb'er.

Example VII sample VIII The apparatus described in Example I was us'edjto prepare finely divided chromium oxide Chromic chloride was passed into the chamber at the rate of 8 liters per hour. & Carbon dioxide was added through the inert gas jetat the rate of 4 liters per 'hour and oxygen wasjintroduced at the rate of 10 liters per minute. lhe reaction vessel was maintained at 1000" C. throughout the reaction, and a finely divided 'chromic oxide was collected. Although the present invention. has been described in connection with the details of certain reaction embodiments "thereof, it is not intended that.

d in Example, I was mizing crystali halides out of substantial contact with hot surfaces within the reaction zone during the major portion of said decomposition.

2. The method of producing. a finely divided pigment which comprises reacting oxygen with vaporized titanium tetrachloride and a chloride of another metal capable of reacting with oxygen and minimizing I crystal formation by main,-

taining the chloride vapors out of substantial contact with hot'surfaces within the reaction 1 zone during the major portion of said decomposition.

3. The method of producing a finely divided, pigment which comprises reacting oxygen with vaporized titanium tetrachloride and a chloride of another metal capableof reacting with oxygen at a temperature of 1400 to 2200" F. with oxygen and minimizing crystal formation by maintaining the chloride vapors out of substantial contact I with hot surfaces within the reaction zone during the major portion of said decomposition.

4. In the process of producing a titanium dioxide containing pigment by reaction of oxygen 7 with a titanium halide and a halide of another metal capable of reacting with oxygen in gas suspension the step which comprises introducing the said halides into the reaction zone through a. nonoxidizing 'gas.

/ 5. A method of producing a titanium dioxide containing pigment which comprises introducing oxygen into one portion of a reaction chamber, introducing titanium tetrachloride and a chloride of another metal capable of reacting with oxygen into a second portion of the chamber and maintaining a body of nonoxidizing gas in said second portion adjacent the chloride inlet whereby substantial decomposition of the chlorides at the inlet is minimized and reacting said oxygen with said chlorides.

6. In the process of producing a titanium dioxide containing pigment by reaction of oxygen with titanium tetrachloride and a chloride of another metal capable of reacting with oxygen in gas suspension the step which comprises introducing the said chlorides into the reaction zone through a nonoxidizing-gas.

7. A method of preparing a titanium dioxide containing pigment which comprises introducing titanium tetrachloride and a halide of another metal capable of reacting with oxygen into a.reaction chamber and minimizing crystal formation by thermally decomposing said chlorides by means of oxygen before substantial contact of the chlorides with hot surfaces within the chamber can occur.

chloride inlet by maintaining a body of a gas -which is substantially unreactive to the chloride adjacent saidlnl'et and thermally decomposing said chlorides before substantial contact'of the chlorides with hot surfaces can'occur. 4

9. As an improvement in the other metal which is capable of reacting with oxygen at high temperatures, while maintaining crystal formation by preventing thermal decomposition .of the halides adjacent hot surfaces, the step which comprises introducing the halides into let substantially i'ree' of oxygen.

suitable for use as 'a 10. The method of.

pigment while minimizing crystal formation which comprises subjecting va- DOrized titanlumtetrachloride and -a' chloride of another metal which is capable of reacting with oxygen to thermal decomposltionwithin a reac- 1 acting a 8.'The method of preparing titanium dioxide which comprises introducing titanium tetrachloride, another metallic chloridewhich is capable of reacting with oxygen, and oxygen into a reaction chamber, maintaining the temperature sumtion chamber by means of oxygen at at'ure not substantially below 1500? r. and mini mizin crystal formation by conducting the de-- composition out-oi substantial contact with hot surfaceswithinthe reaction chamber.

-; 11. In the process of producing a metal oxide by reaction r oxygen with a metallic chloride L 1 which is capable of reacting with oxygen in-gas suspension, the stepwhich comprises introducing the vaporized chloride into the reaction zone through a nonoxidizing gas.

v 12. The. method of producing finely divided oxides of'amphoteric metals which comprises revaporized halide of a metalcapable of forming an amphoteric hydroxide with. oxygen and minimizing crystal formation by maintaining the halide out of substantial contact with the hot surfaces of the reaction chamber dining the major portion of said decomposition.

13. The method of producing afinely divided metal oxide which comprises reacting oxygen with a vaporized metallic halide which is'capable of reacting'with oxygen'and minimizing crystal formation by maintaining the halide vapor out of substantial contact with hot surfaces within the reaction zone during the major portion of said decomposition.

14. In the process'of by reaction-of a metallic halide which is capable of reacting with oxygen in gas suspension, the stepwhich comprises introducing the vaporized halide into the reaction zone through a nonoxidizing 'gas. t

15. A method of producing a finely divided' metal oxide which comprises introducing oxygen into one portion of a ;reactionchamber,'intro- 'ducing a metallic halide which is capable of reacting with oxygen into asecond portion of the chamber and maintaining a body of nonoxidizing gas in said second'portion of the chamber adjacent the halide inlet whereby substantial decomposition of the halide at the inlet is avoided and reacting the oxygen with the halide.

16. The method of producing finely divided metallic oxides which comprises reacting oxygen with a vaporized mixture of metallic halides capable of reacting with oxygen and minimizing the formation of crystals by maintaining the halide vapor out of substantial contact with the hot surfaces within the reaction zone during the major part of the decomposition.

17. A method of producing a finelydivided oxide composition which comprises introducing process of preparing a pigment by thermally-decomposing va- 'porized titanium tetrahalide and 'a halide of anproducing titanium dioxide f a temperproducing a metal oxide oxygen into one portion of a reaction chamber, introducing a mixture of a halide of a metal capable of forming an amphoteric hydroxide and a halide of another amphoteric metal into a second portion ofthe chamber and maintaining a body 'of nonoxidizing gas in said second portion adjacent .the halide inlet whereby substantial decomposition oi the halide at the inlet is avoided. 18; The method of producing a finely divided oxide composition which comprises subjecting a vaporized halide of an amphoteric metal, containing a substantial proportion of a halide of another metal capable of forming an amphoteric hydroxide, to thermal decomposition within a reaction chamber in the presence of oxygen at a temperature sufliciently high to permit rapid and ,substantiallyicomplete conversion of the halides titanium oxide pigment which comprises treating vaporized titanium tetrachloride containing a halide of a metal of the group consisting of chromium, silicon, aluminum, zirconium, antimony, zinc, beryllium, boron, cadmium, cobalt, molybdenum, nickel and vanadium with oxygen at an elevated temperature and maintaining the halides out of substantial contact with the hot surfaces of the reaction chamber.

20. The method of producing finely divided oxides of metals of the group consisting of chromium, silicon, aluminum, zirconium, antimony, zinc, beryllium, boron, cadmium, cobalt, molybdenum, nickel, and vanadium which comprises reacting a vaporized Halide of a metal of said group with oxygen while maintaining the halide out of substantial contact with the hot surfaces of the reaction chamber.

21. The process of claim 13'wherein the halide is a chloride of chromium;

IRVING E. MUSKAT. 

